SK177990A3 - Method of production of alkylmetacrylate - Google Patents

Abstract

A process for the preparation of an alkyl metha­crylate, which comprises:

• a) selectively removing propadiene from a C₃-mixture comprising a mixture of propyne and propadiene that has been obtained from an ethene cracker, a catalytic cracker or an LPG-dehydrogenation process, to afford a propyne feed in which the ratio of propyne to propadiene is ≧ 6, and
• b) contacting the propyne feed with carbon monoxide and an alkanol in the presence of a carboxylation catalyst.

Description

Process for preparing alkyl methacrylate

Technical field

The present invention relates to a process for preparing alkyl methacrylate, in particular methyl methacrylate.

BACKGROUND OF THE INVENTION

Up to now, methyl methacrylate has been industrially prepared mainly _from r>

called. acetone-cyanohydride procedure. The disadvantages of this process are that large amounts of sulfuric acid and ammonium hydrogen sulphate are produced at the same time, which need to be removed or reprocessed, and that other waste material - hydrogen cyanide - is a very toxic substance and increases resistance to storage. and transport (cf. T. Haeberle and G. Emig, Chem. Eng. Technol. 11 (1988), 392-402). In view of the growing objections to environmental damage, great attention has been paid to seeking alternative procedures that would not have the disadvantages mentioned.

One possible alternative procedure, described in 1964 by Y. Sakakibir in Bull. Chem. Soc. Japan 37, 11 (1964) 1601-1609, consists in reacting propyne with carbon monoxide and an alkanol in the presence of a carboxylation catalyst. Although this process has been known for a long time and enjoyed considerable interest, it has never been used commercially.

A factor limiting the commercial use of the carboxylation process was the unavailability of large quantities of cheap propyne as the basic raw material for this process.

For the possible preparation of propyne pov. So, for example, in the Kirk-Othmer Encyclopaedia

2nd Edition, Volume Supplement (1971), many post-chapters of Methylacetylene of Chemical Technology, p. Nos. 547-556 describe various processes including dehydrohalogenation of dibromopropylene, hydration of magnesium carbide, reaction of sodium acetylide with dimethyl sulfate in liquid ammonia, as well as various methods of pyrolysis or cracking.

Of the many potential sources of propyne, as raw material for the preparation of alkyl methacrylates, the cheapest fraction of the 3 carbon atoms appears to arise in the ethene cracker (also known as diesel cracker, diesel gas oil cracker and / or liquid fuel gas cracker). (LPG)), further in a catalytic cracking unit or by dehydrogenation of liquid fuel gas (LPG). A characteristic feature of such a fraction of the components is that it contains a mixture of propyne and propadiene in an approximate 1: 1 ratio. At present, the mixture of propyne and propadiene is usually not separated, but is generally incinerated (either as a fake or a welding gas) or is hydrogenated to propene and propane.

EP-A-0190473 describes a process for the preparation of alkyl acrylates, such as methyl methacrylates, by carboxylation of propadiene. Example 10 of this publication describes an experiment in which methyl methacrylate is prepared by reacting a mixture of propadiene and propyne with carbon monoxide and methanol in the presence of a relatively inactive carboxylation catalyst. Both propadiene and propyne are converted to methyl methacrylate.

The ratio of propyne to propadiene is 1: 1, i. the same ratio as that occurring in the fraction of the C 3 components produced in the ethene cracker, in the catalytic cracker, or by the dehydrogenation of liquid fuel gas (LPG).

SUMMARY OF THE INVENTION

Surprisingly, it has now been found that propadiene is the poison for carboxylation catalysts in the carboxylation of propyne and methanol to yield methyl methacrylate. Moreover, the inactivating effect of propadiene appears to increase as the intrinsic activity of the carboxylation catalyst for propyne carboxylation increases. \

Accordingly, the present invention provides a process for preparing an alkyl methacrylate comprising:

(a) selectively removing propadiene from a mixture of 3 carbon atoms comprising a mixture of propyne and propadiene obtained in an ethene cracker, a catalytic cracker, or by dehydrogenation of liquid fuel gas (LPG) to obtain propyne as a feedstock in which the ratio of propyne to propene propadiene> 6, and

b) contacting the obtained propyne with carbon monoxide and an alcohol in the presence of a carboxylation catalyst.

The mixture of 3 carbon atoms used as starting material in the process of the invention comprises a mixture of propyne and propadiene obtained in an ethene cracker, a catalytic cracker, or dehydrogenation of liquid fuel gas (LPG). Ethene cracking units, catalytic cracking units and liquid fuel gas dehydrogenation processes are known.

Thus, the ethene cracker is a cracker in which ethene is prepared by thermal cracking from hydrocarbon fractions such as diesel, gas oil, liquid fuel gas (preferably isobutane) or ethane. The catalytic cracking unit is a cracking apparatus in which hydrocarbons are prepared by catalytic cracking of hydrocarbon fractions, such as heavy gas oil or vacuum distillates. The LPG dehydrogenation process is a process in which propane is converted to propene either thermally or catalytically.

Each of these methods provides, inter alia, a fraction of 3 carbon atoms, consisting predominantly of 3 carbon atoms, in particular propane, propene, propyne and propadiene.

The fraction of the C 3 components preferably comprises a mixture of propyne and propadiene obtained from an ethene cracker.

The 3-carbon fraction used in the process of the invention may be a mixture of 3-carbon components obtained in an ethene cracker, a catalytic cracker, or a liquid fuel gas dehydrogenation process. However, it is preferably a mixture derived from such a fraction by a process in which the concentration of the mixture of propyne and propadiene has been increased. It can be, for example, a mixture formed from a fraction of 3 carbon atoms, by distilling off propane and / or propene, by selective solvent washing and / or by adding further propyne and / or propadiene. Further propyne and / or propadiene can be added, for example, by recycling, which will be described in more detail below.

In some cases, it will be very advantageous to combine mixtures of propyne and propadiene obtained from several different ethene cracker units, catalytic cracker units and / or from liquid fuel gas dehydrogenation (LPG) processes which can be obtained at different refineries. Such mixtures are most preferably conveyed in concentrated form.

A preferred method of recovering a mixture of 3 carbon atoms from an ethene cracker is that comprising using at least a portion of the crude 3 carbon atom fraction obtained from a depropanizer (a propane removal apparatus) (a distillation column where hydrocarbons are separated) with 3 carbon atoms from higher hydrocarbons], bypassing the hydrogenation apparatus (where normally propyne, propadiene and part of the propene is hydrogenated to a propane / propene mixture and then the mixture is fed to a propane / propane separator to obtain propene of a suitable propene for the polymerization, as a product taken from the top of the column and substantially pure propane as a product taken from the bottom of the column), and this fraction is introduced directly into the apparatus for separating propane from propene. In this embodiment, it is advantageous to operate said propane-propene separation apparatus under slightly different conditions than those of the above-described hydrogenation to accommodate the fact that at least a portion of the feed to this apparatus still contains a small amount of propyne and / or propadiene, since this fraction was not subjected to pre-hydrogenation. The operation of the separation apparatus will then be such that the upper fraction of the separation apparatus will still contain propene of a quality suitable for polymerization, albeit at a lower yield, and part of the propene will leave the lower separation apparatus with a stream mainly consisting of propane and propene. (about 70%) and also includes propadiene and propyne in approximately equimolar ratios.

It is advantageous to minimize as much inert or quasi-inert materials in the propyne feedstock so as to maximize collapsing in a plant having a fixed capacity at a given catalyst efficiency. According to a preferred embodiment of the invention, the mixture of propyne and propadiene in the fraction of the three carbon atoms is concentrated by selective solvent washing to obtain a solvent stream comprising a mixture of the three carbon atoms. For example, a mixture of propyne and propadiene can be obtained from a fraction leaving the bottom of a separator for separating propane from propene, the fraction containing a considerable amount of propane, propene, propyne and propadiene. The scrubbing is preferably carried out in a column under elevated pressure (0.2 to 2.0, preferably 0.6 to 1.2 MPa), using countercurrent organic solvent flows and a stream flowing from the bottom of the separator for separating propane from propene, so that it is discharged as the upper fraction stream. Consisting essentially of propane and propene and containing> 0,2% of a mixture of propyne and propadiene.

The solvent which absorbs propyne and propadiene at the elevated temperature used preferably includes polar organic solvents such as an amide, e.g. dimethylformamide, dimethylacetamide or N-methylpyrrolidone, nitrile such as acetonitrile, sulfone such as sulfolane, or a mixture thereof, especially dimethylformamide. Another preferred extraction solvent is an alcohol such as methanol, which is preferably present in an amount such that it is used as one of the reactants in the subsequent carboxylation reaction, thereby simplifying the process.

Propadiene can be selectively removed by chemical processes such as isomerization to propyne and / or by physical processes such as distillation, preferably by extraction distillation.

Isomerisation of propadiene to propyne is a chemically equilibrium reaction that is well known. The state of chemical equilibrium depends on temperature. As the temperature rises, the proportion of propadiene also increases. At room temperature, an isomerization ratio of propyne to propadiene of about 9: 1 is achieved.

The isomerization is usually carried out in the gas or liquid phase in the presence of an isomerization catalyst at a temperature in the range of -30 to 100 ° C, preferably at a temperature of 0 to 40 ° C, particularly preferably at a temperature of 10 to 30 ° C, and at pressure in the range of from 0.01 to 10.0 MPa, particularly preferably at a pressure of from 0.1 to 2.0 MPa.

Catalysts suitable for the isomerization of propadiene to propyne are known. So eg. the isomerization catalyst may comprise an alkali metal or an alkali metal oxide deposited on alumina, such as a mixture obtainable by heating an alkali metal carbonate deposited on an alumina carrier, preferably potassium carbonate on gamma alumina, in an inert atmosphere, or a mixture obtained by depositing at least one molten alkali metal on alumina, preferably a low melting eutectic mixture of sodium and potassium on alumina. Suitable isomerization catalysts are also described in the publication

Kirk-Othmer, Encyclopaedia of Chemical Technology, 2nd edition,

Volume Supplement (1971), pp. 547-556 and U.S. Pat. No. 3,771,605.

In general, the efficiency of the isomerization catalysts decreases with decreasing temperature. Thus, when the desired propyne feedstock is to be prepared in which the ratio of propyne to propadiene is> 10, especially> 20, it is preferable to remove the propadiene from the mixture of 3 carbon atoms by physical processes.

Once the propadiene has been removed by physical processes, propyne can be reacted with carbon monoxide and an alcohol to form an alkyl methacrylate. However, it is preferably isomerized to a mixture of propyne and propadiene and recycled to step a) or step b) of the process. Optionally, the isomerization product is subjected to distillation to remove heavy components prior to recycling to step a) or step b).

Extractive distillation is a known method for removing a component from a mixture containing two very similar components. To remove propadiene from the mixture of propyne and propadiene, the mixture of propyne and propadiene is dissolved in a polar organic solvent and the propadiene is removed as a gas (e.g., by stripping) to leave propyne dissolved in the solvent. Suitable solvents are amides, e.g. dimethylformamide or N-methylpyrrolidine, nitriles such as acetonitrile, sulfones such as sulfolane and alcohols such as methanol. Preferred solvents are dimethylformamide, N-methylpyrrolidine, methanol and mixtures thereof.

It should be pointed out that by combining the physical separation step to remove propadiene with the isomerization step, the entire amount of propyne and propadiene in the original mixture of the 3 carbon atoms can essentially be converted to an alkyl methacrylate. This combination of process steps is therefore a particularly advantageous feature of the invention.

If the mixture of the three carbon atoms has been obtained by solvent washing, the propadiene is preferably stripped from the solvent stream containing propyne and propadiene to obtain propyne as feedstock. This stripping is possible because propadiene and propyne have different volatility and solubility in solvents. The stripping may advantageously be carried out in a column utilizing indirect heat exchange for the main absorption column, downstream of the column. The propyne can then, if desired, be separated from the solvent in another column. The stripping operation can be controlled so that the propadiene content of the propyne as in the base feedstock is almost zero.

In the process according to the invention, the molar concentration of propyne in the propyne feedstock is preferably above 35%, particularly preferably above 50%, even more preferably above 90%, and most preferably this concentration is at least 99%. The feed preferably contains at most 10 mol% propadiene and at least 35 mol% propyne.

The propyne feed contains at least 50% by weight. a combination of propyne and propadiene, particularly preferably at least 60% of this combination, and most preferably at least 80% of this combination.

The propyne feed preferably contains at least 50%, particularly preferably at least 90%, by weight of the hydrocarbons having 3 carbon atoms.

In the process of the present invention, a propyne feed in which is at least 8, in particular > 20 and especially > The carboxylation catalyst is a feed in which this ratio is most preferably > 10,000.

The carboxylation catalyst of the invention may be any of the propyne carboxylating promoters.

It is preferable to use a propine to propadiene ratio. When using highly active, it is preferred to use a propyne of > 500, particularly preferably > 1000, and used in the process according to the present invention. groups of the periodic table, particularly preferably a palladium catalyst.

The carboxylation catalyst is preferably based on a mixture of compounds VIII. groups of the periodic system of elements (e.g. palladium) of a ligand (e.g. monodentate or quasi-bidentate phosphine, arsenic, stibine or the like containing nitrogen) and an anion of Brenenstendic acid (from salt, ester, anhydride or acid, and preferably not too strongly coordinating) . A particularly preferred example of such a catalyst is a catalyst based on a mixture of a palladium compound, an organic phosphine of the formula PR ³ , wherein each R is independently an optionally substituted hydrocarbon radical or heterocyclic radical and not a hydrogen halide Broenstendic acid having a pK? second

The hydrocarbon group in the optionally substituted hydrocarbon group is preferably an alkyl group, for example an alkyl group having 1 to 6 carbon atoms such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl or tert-butyl, cycloalkyl, e.g. cyclopentyl or cyclohexyl or aryl such as phenyl or naphthyl. Alternatively, the two R substituents may be an optionally substituted alkylene chain.

The heterocyclic group in the optionally substituted heterocyclic radical is preferably an aromatic group containing an imine nitrogen atom, for example pyridyl, pyrazinyl, quinolyl, isoquinolyl, pyrimidinyl, pyridazinyl, cinolinyl, triazinyl, quinoxalinyl or quinazolinyl. The nitrogen atom of the imino group in the aromatic group containing the imine nitrogen atom is preferably bound to the phosphorus by a single bridging nitrogen atom, such as in the case of

2-pyridyl, 2-pyrazinyl, 2-quinolyl, 1-isoquinolyl, 3-isoquinolyl,

2-pyrimidinyl, 3-pyridazinyl, 3-quinolinyl, 2-triazinyl, 2-quinoxalinyl and 2-quinoazolinyl.

Examples of optional substituents that may be present in an optionally substituted hydrocarbon group or heterocyclic group include halogen atoms such as fluorine, chlorine or bromine; alkyl groups such as methyl or ethyl; haloalkyl groups such as trifluoromethyl; alkoxy, for example methoxy or ethoxy; haloalkoxy, for example trifluoromethoxy; acyl groups such as acetyl; acyloxy groups such as acetoxy; amino groups such as dimethylamino; hydroxyl groups; nitrile groups; acylamino, for example acetamido; as well as aryl groups such as phenyl.

Examples of Broensted acids with the exception of hydrohalic acids include sulfuric acid, sulfonic acids such as p-toluenesulfonic acid, naphthalenesulfonic acid, trifluoromethanesulfonic acid, chlorosulfonic acid, fluorosulfonic acid or sulfonic acid orthophosphoric acid, phosphoric acid orthophosphoric acid, ; carboxylic acids such as trifluoroacetic acid; halogenated acids such as perchloric acid, hexafluoro-silicic acid; HBF ₄ , HPF _g or HSbFg.

Examples of such catalysts are disclosed in European patent applications EP-A-186228 and EP-A-271144, for example a combination of (a) palladium acetate, (b) triphenylphosphine, tris (p-methoxyphenyl) phosphine or diphenyl-2-pyridylphosphine and (c) ) toluenesulfonic or trifluoroacetic acid.

The reaction between propyne, alcohol and carbon monoxide is preferably carried out at a temperature in the range from 20 to 200 ° C, even more preferably at a temperature in the range from 20 to 80 ° C and at a pressure in the range from 0.5 to 7.0 MPa. The additional solvent is not essential to the reaction. However, an alcohol ester may suitably be used as the solvent.

When the carboxylation catalyst is a metal catalyst VIII. Preferably, the catalyst has conversion efficiency in the absence of propadiene propyne / g catalytic metal / h, more preferably / g catalytic metal / h, particularly preferably at least 5,000 and most preferably 10,000 g propyne / g catalytic metal / h. This is approximately equivalent to the production of 25 kg methacrylate / g catalytic metal / h if the catalyst metal is palladium and the methacrylate is methyl methacrylate.

not less than 100 g of 1000 g of propyne

The alkyl methacrylate produced by the process of the present invention is suitably an alcohol ester containing up to 20 carbon atoms, preferably 1 to 4 carbon atoms. Examples of alcohols include methanol, ethanol, propanol, isopropyl alcohol, butanol, isobutyl alcohol and tert. butanol. The most preferred alkanol is methanol which provides methyl methacrylate as the product.

A suitable and attractive method for carrying out the carboxylation reaction involves a process in which the propyne feed is combined with a mixture of fresh alkanol and a recycled stream of azeotropic methacrylate / alcohol mixture and then simultaneously fed to a reactor with a catalyst solution and carbon monoxide.

This procedure is described below using methanol as the preferred alkanol. Very preferably, the propyne feed is fed to a mixing device, for example a tank, where it is combined with a mixture of fresh methanol and a recycled stream of azeotropic mixture of methyl methacrylate and methanol, and then fed to the reactor, and the catalyst solution is also fed to the reactor. The catalyst solution can be fed to the reactor using a carbon monoxide feed line or separately. The resulting stream leaving the reactor is isothermally freed of unreacted gas residues. This gas stream can be cooled (down to about -20'C) to obtain valuable, low volatile components that return to the liquid feed. Uncondensed gas (mainly carbon monoxide) is removed and used differently, for example as a fuel gas. Any unreacted propyne present may be washed with methanol and recycled to the reactor. The liquid fraction containing product, catalyst residues and heavy components is fed to a distillation column.

The overhead stream, which consists of an azeotropic mixture of methyl methacrylate and methanol, is recycled to the feed mixer and subsequently to the reactor. The stream from the bottom of the column is suitably passed to a second distillation column. The top product of this second distillation column is pure methyl methacrylate, while the bottom product of this distillation column contains catalyst residues and heavy components. The obtained methyl methacrylate can be isolated in a stripping column to remove the heavy components and returned to the second column. The concentrated residue may be treated for reuse or removal accordingly.

DETAILED DESCRIPTION OF THE INVENTION

In the following, the invention is illustrated in more detail by the following examples. Example 1 illustrates a process in which a mixture of 3 carbon atoms, which is typical of a mixture of 3 carbon atoms from a cracking unit, is converted to a propyne feed by washing with solvent followed by expulsion of propadiene. Example 2 illustrates a process wherein propadiene isomerized on an isomerization catalyst to produce propyne. Examples 3 and 4 illustrate the carboxylation of propyne to give methyl methacrylate. The comparative examples demonstrate the surprising inhibitory effect of propadiene on propyne carboxylation.

Example 1

Fresh feed, consisting of 52.7% mole. propane,

I. 6 mol% propylene, 19.1 mol%. propadiene and 25.1 mol%. propyne and 1.5 mole%. of heavy hydrocarbons, combined with the recycle stream from the propadiene isomerization reactor and fed to an absorption column. If necessary, the feed into the distillation column is first carried out to remove high-boiling impurities. The combined mixture contains 45.4% propane, 10.5% propylene,

II. 4% propadiene and 32.7% propyne.

In the absorber, the combined mixture is contacted with dimethylformamide (2.8 kg of dimethylformamide / kg of combined mixture). The pressure in the absorber is 0.8 MPa and the absorber has a cooker and a cooler. The liquid product from the top of the absorber is 96.8% propane, 3.0% propylene, 0.2% propadiene-propyne. The product from the bottom of the absorber is 68.3% dimethylformamide, 4.8% propadiene and 14.2% propyne, 8.6% propane and 4.1% propylene.

This mixture is cooled to 35 ° C and fed first to a reboiling and cooler stripper operating at 0.26 MPa to remove all propane, propylene, propadiene, and a portion of propyne to give a bottom column product from 88.1% dimethylformamide and 11.9% methylacetylene with only 10 ppm propadiene. The product removed from the top of this column consists of 38.2% propane, 18.3% propylene, 21.5% propadiene and 22% propyne, and is fed to a propadiene isomerization reactor containing an isomerization catalyst and where part of the propadiene is converted to propyne to obtain a product containing 4.4% propadiene and 39.1% propyne. This product is recycled by a stream that is combined with fresh feed.

The product discharged from the bottom of the column is fed to a second stripper column containing a reboiler and a cooler operating at a pressure of 0.16 MPa. The product taken from the top of this stripping column consists of propyne containing only 80 ppm propadiene. The product taken from the bottom of this stripping column consists of dimethylformamide containing 0.5% propyne. This product is reused in the first absorber after cooling. The role of coolers in stripping columns is not only to condense the hydrocarbon vapors, but also to remove dimethylformamide from the hydrocarbon product.

Example 2

Preparation of the catalyst

Catalyst containing 20 wt. Potassium carbonate on alumina is prepared as follows:

250 g of cylindrical bodies of gamma-alumina (gamaalumina) with a diameter of 1.59 mm (pore volume 0.7 ml / g) are activated for 16 hours at 500 ° C.

- 50 g of potassium carbonate are dissolved in 150 ml of demineralised water at room temperature.

- 200 g of activated gamma-alumina are brought into contact with the above-mentioned potassium carbonate solution and mixed well (starting moisture method).

After impregnation, the catalyst is dried at 125-140 ° C for 16 hours. Before use, the catalyst thus obtained containing 20 wt. potassium carbonate on gamma alumina activated under nitrogen atmosphere at 575 ° C for 24 hours.

Isomerisation of propadiene

The propadiene is isomerized to propyne in a packed bed reactor containing catalyst activated potassium carbonate on gamma alumina as follows:

- a tubular reactor with stainless steel tubes with an internal diameter of 0.9 cm is charged with 2.0 g of potassium carbonate catalyst bodies on gamma alumina.

- the catalyst is activated by the described thermal process.

The reactor is brought into operation and a mixture of liquefied C 3 and C 4 hydrocarbons is pumped through the catalyst. The feed contains 15% by volume of propadiene, 22% by volume of propyne, 49% by volume of propene, 5% by volume of propane, 3% by volume of 1,3-butadiene, and a minor amount of other C 3 -C 4 hydrocarbons.

An isomerisation equilibrium of propyne / propadiene is formed at an hourly liquid velocity of up to 10 l (feed) / l (reicator) h. The concentration of propyne and propadiene in the reaction product of the feed described is 33.7% v / v and 3.3% v / v when the reaction is carried out at 25 ° C.

Example 3

250 ml autoclave equipped with a magnetic stirrer from

0.1 mmol of palladium acetate, 1 mmol of tri- (p-trifluoromethylphenyl) phosphine, 1 mmol of methanesulfonic acid, 10 ml of methanol and 40 ml of anisole are charged.

The air is then evacuated and 30 ml of propyne is added. Subsequently, carbon monoxide is introduced until a pressure of 2.0 MPa is reached. The autoclave is then sealed and heated to 90 ° C. After completion of the reaction, the contents of the autoclave are analyzed by liquid-phase gas chromatography. The reaction rate is 40 g propyne / g palladium / h.

Comparative example

The procedure is as in Example 3, but using 15 ml propyne and 15 ml allene. The reaction rate is 4 g propyne / g palladium / h.

Example 4 £

A 300 ml stainless steel autoclave with a magnetic stirrer was successively charged with 0.025 mmol of palladium acetate, 1 mmol of bis (6-methyl-2-pyridyl) phenylphosphine, 2 mmol of p-toluenesulfonic acid, 30 ml of N-methylpyrrolidine and 30 ml of methanol. . Air is then evacuated from the autoclave and then 25 ml of propyne is added. Carbon monoxide up to 6.0 MPa is then fed into the autoclave. The autoclave is then sealed and the contents of the autoclave heated to 80 ° C. After a reaction time of 1.5 hours at 80 DEG C., a sample of the reactor contents is analyzed by liquid-phase gas chromatography. The average conversion rate is 7500 g propyne / g palladium / h.

Comparative Example

The procedure is as in Example 4, but using 20 ml of propyne and 10 ml of propadiene instead of 25 ml of propyne. The reactor contents are only heated to 60 ° C. There is no reaction. The reactor contents are then heated to 80 ° C. Again, no reaction was observed. Finally, the Rector's content is heated to 100'C. The reaction is started at this temperature. The reaction time is 5 hours. The average conversion rate is only 200 g propyne and propadiene / g palladium / h.

Claims (10)

PATENT CLAIMS A process for the production of alkyl methacrylate, characterized in that from a mixture of 3 carbon atoms comprising a mixture of propyne and propadiene obtained in an ethene cracker, a catalytic cracker or dehydrogenation of a liquid fuel gas, propadiene is selectively removed to form propyne. feed, wherein the ratio of propyne to propadiene is> 6, wherein the propyne feed is contacted with carbon monoxide and an alkanol in the presence of a carboxylation catalyst. 2. The process according to claim 1, wherein the mixture obtained in the ethylene cracker is used as a mixture of 3 carbon atoms, comprising a mixture of propyne and propadiene. 3. A process according to claim 1 or 2, wherein the mixture of 3 carbon atoms comprising a mixture of propyne and propadiene obtained in the ethene cracker using at least a portion of the stream of 3 carbon atoms obtained from the depropanizer is directly fed to the apparatus. separating propane from propene and isolating the product taken from the bottom of the apparatus. 4. A process according to any one of Claims 1 to 3, wherein the mixture of propyne and propadiene in the mixture of 3 carbon atoms is concentrated by selective scrubbing with a solvent to obtain a solvent stream comprising a mixture of 3 carbon atoms. 5. The process of claim 4, wherein methanol or mixtures thereof is used. Αχ'ατΪζτ 6. The process according to one of the claims 1 to 5, characterized in that the propadiene is removed by extractive distillation. 7. The process of claim 4 or claim 4 wherein the propadiene is stripped from the solvent stream. 8. The process of item 6 or 7, wherein the removed propadiene is contacted with an isomerization catalyst to convert to propyne, and the isomerization product is recycled to step a) or b). 9. The process of claim 8, wherein the isomerization catalyst is an alkali metal or alkali metal oxide catalyst on alumina. Method according to one of boxes 1 to 9, characterized in that the propyne feed contains at least 99 wt. propyne. Method according to one of the preceding claims, characterized in that the feed ratio is> 100. - points 1 to 10 characterized by propyne to propadiene in propyne The method according to one of the claims, characterized in that the catalyst is based on elements. wherein the carboxylation catalyst used is a metal VIa. groups of the periodic system The method of item 12 is characterized as a metal catalyst VIII of the array of elements using a catalyst in that the periodic base groups are palladium. Process according to one of the preceding claims, characterized in that methanol is used as the rf point of the alkali 13y.